Pipe recovery logging



Filed July 28, 1966 EQUIP.

PROC.

2 Sheets-Sheet 1 lfmm'llllu RECORDER I a 77 v 40 52 ,f

INVENTORS MIKE DAVIS ARTHUR 8. WINTER ATTORNEY FBG.

United States Patent 3,404,563 PIPE RECOVERY LOGGING Mike Davis, and Arthur B. Winter, Houston, Tex., assiguors to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Filed July 28, 1966, Ser. No. 568,520 6 Claims. (Cl. 73-151) ABSTRACT OF THE DISCLOSURE A stuck pipe recovery logging instrument which uses an acoustic section in conjunction with a density-measuring section to provide verification of the location of stuck pipe. The tool is also provided with a plurality of explosive charges to permit disengagement of the free portion of the drill pipe on the same logging run. A drill pipe collar locator section provides positive depth identification.

This invention relates to a method of and a system for determining the point or points at which drill pipe is stuck in a borehole and includes means for disengaging the free portion of said drill pipe on the same trip into the borehole.

In the drilling of petroleum wells, occasionally the drill pipe will become stuck in the borehole. Several and various causes contribute to this condition, such as wall sticking, lost returns, heaving shale and blowout, all of which are well known to the drilling industry. In such cases, it is not possible to further rotate or logitudinally move the drill pipe with the drilling equipment av.ail .able at the well site. Presently, it is customary to locate the last point from the surface at which the drill pipe is free. After locating such free point, an explosive charge is discharged in a tool joint or collar above the free point. The explosive charge will usually enlarge the tool joint sufficiently to permit the free portion of the pipe to be backed out of the tool joint and withdrawn from the borehole. Fishing and wash-over operations are then performed to remove the remainder of the drill pipe from the borehole.

One method of locating the free point is disclosed in P. W. Martin, US. Patent 2,530,309. This method requires the entire string of drill pipe to be put in tension or torsion while the free point is being located. A subsequent development disclosed in J. C. Bender, US. Patent 2,686,039, discloses a similar means of locating the free point, but includes the provision of an explosive charge which may be used for back-off purposes during the same run in the borehole. However, in both cases, it is necessary to maintain tension or torsion on the drill pipe during the locating operations, and the only point that can be determined is the last free point.

In actual practice, there may be a number of stuck points below the last tree point; these stuck points may cause trouble during the subsequent fishing and washover operations utilized to retrieve the portion of the drill pipe remaining in the borehole after the free portion has been withdrawn. Moreover, the determination of the free point is a rather tedious procedure and requires numerous stop-and-go operations and a considerable amount of skilled know-how.

It is an object of the present invention to provide a method of and a system for making a continuous log of the entire drill pipe to determine all points at which the drill pipe is stuck.

It is another object to provide a continuous pipe recovery logging system which does not require the drill pipe to be placed in tension or torsion during the logging operations.

'ice

It is a further object to provide a continuous pipe recovery logging system which provides two different types of measurement so that the location of stuck points may be verified.

It is still a further object to provide a continuous pipe recovery logging system which is provided with at least one explosive charge so that back-off operations may be performed on the same trip into the borehole.

The pipe recovery logging system of the present invention is comprised of a downhole tool having an acoustic amplitude section which measures the attenuation of the amplitude of the first arrival of an acoustic wave, a collar locator section which provides positive depth identification, and a density section which measures the density of the material surrounding the drill pipe. The downhole tool is also provided with a plurality of explosive charges which may be discharged in a collar on the same run in the borehole to permit disengagement of the free portion of the drill pipe.

The system is provided with surface gear which processes and records the indications from the downhole tool and provides controls for the firing of the explosive charges.

The downhole tool is first run to the bottom of the drill pipe. The suspected section of drill pipe is then logged and an examination of the log is made to determine the stuck points. From such determination, an appropriate collar is chosen and an explosive charge fired. The acoustic and density measurements complement and supplement each other as well as providing a verification of the conditions around the drill pipe.

Other objects and objects directed to details of manufacture, construction and use will be apparent from the detailed description which follows in which:

FIG. 1 is a diagrammatic cross-section of a borehole having a drill pipe which is stuck at several points along its length. The downhole tool of the present invention is shown in the drill pipe.

FIG. 2 is a diagrammatic view of a log indicating the points at which the drill pipe is stuck in FIG. 1.

FIG. 3 is a crosssectional view of the downhole tool.

FIG. 4 is a block diagram of the major components of the downhole tool of the present invention.

FIG. 5 is a schematic of the wiring for the discharging of the explosive charges.

Reference will now be had to the drawings where it can be seen that FIG. 1 illustrates a cross section through an earth formation in which a borehole 10 has been drilled. A portion of the borehole 10 is provided with a length of casing 12. The remainder of the borehole v10 is open hole. A string of drill pipe 14 extends through the casing 12 and into the open hole portion of the borehole 10. It can be seen that the drill pipe 14 is stuck at several locations 16, 18 and 20 along the length of the borehole 10 below the bottom of the casing 12. In order to recommence drilling operations, it is necessary to free the drill pipe 14 from its stuck condition.

One common method of doing this in the industry today is to locate the last point from the surface at which the drill pipe 14 is free, remove the free portion of the drill pipe 14 and then wash over and fish out the remainder of the drill pipe 14. To accomplish this under present methods, the drill pipe 14 is placed in stress and a downhole tool is placed inside the drill pipe 14 to determine the last point at which such applied stress can be determined. If the well being drilled is deep and the stuck point is at a considerable depth, it can be seen that the amount of stress near such points will be very small and, therefore, it is difficult to determine the exact point at which the drill pipe 14 is still free. Since the method of determining the free point depends upon locating the point at which stress applied at the surface can still be determined below the surface, it is only the last free point from the surface which can be located. However, as can be seen in FIG. 1, the drill pipe 14 is also stuck at points 18 and 20 which are below the stuck point 16. It is beneficial for subsequent operations to know the other points at which the drill pipe 14 is stuck.

After the last free point has been found, an explosive charge is usually discharged in a tool jointer collar 21 located near the last free point. The force of the charge will usually expand the collar 21 sufficiently to allow the free portion of the pipe to be backed out of the collar and then withdrawn from the borehole 10. After the free portion of the drill pipe 14 has been removed from the borehole 10, it is necessary to go into the borehole and perform wash-over and fishing operations to remove the remaining portion of the drill pipe 14. These operations are often accomplished by using a wash-over tool which fits over the drill pipe 14 and is provided with an end that cuts away the material causing the sticking. A fishing tool is then used to withdraw the free portion of the pipe. However, if the pipe is stuck at several points below the last free point, the wash-over and fishing operations are more difficult, particularly if such points are unknown. Therefore, it is desirable that not only the last free point be known but; also that all stuck points be known so that appropriate plans can be made for proper wash-over and fishing operations. It is the purpose of the present invention to provide such indications.

The system of the present invention is comprised of a downhole tool 22, and a cable 24 which supports the downhole tool 22 in the borehole 1t) and appropriate surface processing and recording equipment 25.

The downhole tool 22 is a suitable pressure housing containing an acoustic amplitude section 26, a collarlocator section 28, and a density section 30. These sections provide indications which are transmitted by a conductor 32 in the cable 24 to the surface where they are processed and recorded by the surface equipment 25 to produce a log 34. In addition, the downhole tool 22 is provided with a plurality of explosive charges 36 which may be discharged by appropriate controls in the surface equipment 25 as will be explained subsequently.

The acoustic section 26 of the downhole tool 22 provides an acoustic signal which is processed by the surface equipment 25 and recorded on the log 34 as an acoustic amplitude curve 38 providing an indication of the attenuation of the amplitude of the first arrival of an acoustic wave. It has been found that the amplitude of the first arrival is effected by material surrounding the drill pipe 14 and accordingly when solid material builds up around the drill pipe 14 in a manner sutficiently to stick it, the acoustic amplitude curve 38 will be attenuated as can be seen in FIG. 1 at locations 40, 42 and 44 which are opposite stuck points 16, 18 and 20.

The collar-locator section 28 provides signals which indicate the various collars 21 in the string of drill pipe 14 as can be seen from the collar curve 48 in FIG. 2. The collar log 48 provides correct and proper depth correlation for the log 34.

The density section of the downhole tool 22 provides a signal indicating the density of the material surrounding the drill pipe 14. This signal is processed by the surface equipment 25 and recorded on log 34 as a density curve 50. When material builds up in such a manner as to cause sticking of the drill pipe 14, it is usually denser than the mud and other materials in the borehole. Accordingly, the density curve 50 reflects changes in density as can be seen at points 52, 54 and 56, which are opposite the stuck points 16, 18 and 20.

As mentioned, the acoustic amplitude section 26 responds to the bonding of the drill pipe 14 by material outside of it. However, in some cases although the build up of material outside the drill pipe is sufiicient to cause the drill pipe to be stuck, a good mechanical bond is not 4 established and, therefore, the acoustic amplitude curve 38 will not reflect a stuck point. In such case, the density section 30 which is sensitive to the density of material surrounding the drill pipe should be responsive to the build up of material and, therefore, the density curve 50 should reflect the stuck condition. In other words, the density curve 50 complements the acoustic curve 38 and by using a different criteria can pick stuck points missed by the acoustic amplitude curve 38. However, since the density curve 50 is responsive to density and in certain instances the density of the materials building up around the drill pipe may be the same as the density of the mud or other materials in the borehole 10, it may in some instances not refiect a stuck point. In such cases, the acoustic amplitude log will supplement the density log. Accordingly, the two logs in conjunction should reflect all of the stuck points.

Accordingly, it can be seen from the log 34 in FIG. 1 that the last point at which the drill pipe 14 is free is just above the stuck point 16. Accordingly, the downhole tool 22 can then be repositioned in the drill pipe 14 so that one of the explosive charges 36 is opposite the collar 58 which is above the first stuck point 16. Discharge of the explosive charge 36 will cause the collar 58 to expand sufliciently to permit the free portion of the drill pipe 14 above the collar 58 to be backed out of the collar 58 and extracted from the borehole 10. A control 60 in the surface equipment 25 is provided for detonation of one of the explosive charges 36 when such charge has been positioned opposite the proper collar.

A preferred embodiment of the acoustic amplitude section 26 of the downhole tool 22 can be seen in FIG. 3 wherein there is shown an acoustic transmitter 62 which repetitively produces a high frequency acoustic impulse. Spaced from the acoustic transmitter 62 by an acoustic isolator 64 is an acoustic receiver 66. The high frequency acoustic impulse produced by the acoustic transmitter 62 travels through the borehole fluid into the formation and back through the borehole when it is picked up by the acoustic receiver 66. The signal received by the acoustic receiver 66 is transmitted to an electronic section 67 where it is amplified and converted into an electrical signal which is transmitted to the surface by the conductor 32 in the cable 24. The electronic section 67 also contains a pulse for repetitively applying pulses to the transmitter 62. At the surface, the electrical signal is fed into the processing and recording surface equipment 25 and, as is well known in the acoustic amplitude art, the amplitude of the first arrival is discerned and recorded as the acoustic amplitude curve 38 on the log 34.

FIG. 3 also discloses a preferred embodiment of the collar-locator section 28. As can be seen, the collarlocator section 28 is comprised of one coil 68 positioned between two permanent magnets 70. The magnet coil produces an electromagnetic field which is disrupted by any discontinuity in the drill pipe 14 such as the collars 21. The collar-locator section 28 is generally similar to the collar locator fully disclosed in Fagan, U.S. Patent No. 2,558,427. Other collar locators, such as disclosed in Peterson, U.S. Patent 2,967,994 may also be utilized if so desired. The signal produced by the collar-locator section 28 each time it passes a collar 21 is processed and transmitted to the surface through conductor 32 of cable 24. At the surface, it is fed into the processing and recording surface equipment 25 and recorded on the log 34 as collar curve 48. The collar curve is correlative of the depth and permits the downhole tool 22 to be properly repositioned after the various stuck points are ascertained.

The density section 30 is also shown in FIG. 3 where it can be seen that the density section is comprised of a source of gamma rays 74 and a suitable detector 76 of emanating radiation, such as a geiger counter, spaced from the source 74 and shielded therefrom. The source 74 is collimated so as to direct the radiation upward and toward the wall of the drill pipe 14. The signals received by the detector are processed in the downhole electronic section 77 containing a power supply and amplifier for the detector 76 and then transmitted over the conductor 32 of the cable 24 to the surface processing and recording equipment 25 where it is recorded on the log 34 as density curve 50 which again is correlated as to depth with the collar curve 48.

The explosive charges may be formed of several separate lengths of coiled primacord 78 positioned at the bottom of the backoflf shot section of the downhole tool 22. Each length of primacord 78 is provided with a separate blasting cap 80. Ignition of the blasting caps 80 is accomplished by energizing them into electrical power; discharge of the blasting cap 80 ignites and discharges the primacord 78. The discharge of the explosive charges 36 can be very detrimental to personnel if the charge be accidentally discharged and therefore it is desirable that provision be made so that accidental discharge is prevented in a positive manner.

One method which has been used to fire downhole charges in tools using DC electrical power for other purposes has been to use DC power of opposite polarity. However, in the present tool both polarities of DC power are used for adjusting sensitivity. FIG. 5 illustrates the system used in the present tool. As can be seen, the blasting cap 80 is discharged by the application of AC power from source 82. However, there is not a complete circuit between the AC power and the blasting caps, therefore, it is necessary to just complete the circuit. This is accomplished by closing spring biased switch 84 and relay 86 which completes the circuit. A condenser 88 prohibits the application of DC power to the blasting caps 80. The switch 84 is spring biased open and must be held in the firing position. With the circuit completed spring biased switch 90 is closed and AC then flows through the circuit and through transformer 92 energizing impulse switch 94 which applies low energy AC power to one of the blasting caps 80. A second application of AC changes the position of the impulse switch 94 so that energy can be applied to the second blasting cap 80. Accordingly, the blasting caps 80 cannot be energized Without first closing the spring switches 84 and 90 and therefore accidental discharge should be eliminated.

In operation, the downhole tool 22 is run through the drill pipe 14 until it reaches the bottom. The acoustic amplitude section 26 and the power supply for the detector 76 of the density section 30 and the casing collarlocator section 28 are then energized. The tool 22 is then withdrawn upward through the drill pipe while the various sections are performing their functions. The acoustic amplitude section 26 provides the necessary information to obtain the acoustic curve 38. The casing collar section '28 provides the collar log 48 and the density section 30 provides the density curve 50. The log is then inspected to determine the stuck points which, as can be seen from FIG. 2, clearly show up as deflections in the various curves. Having determined the last point from the surface at which the pipe is free, the back-off section is positioned opposite the appropriate collar. The back-off section can be properly positioned by counting the collars 21 from a known position. Once the back-off section is positioned in the proper collar, stress is put upon the pipe 14 at the surface. By proper application of the switches 84 and 90, AC power is provided to blasting caps 80 so that the back-off shot is fired which causes a momentary enlargement of the joint permitting the free portion of the drill pipe 14 to be twisted free from the collar and then withdrawn from the borehole 10. Knowing the additional stuck points from the log, subsequent fishing and wash-over operations to free the remaining portion of the drill pipe may be performed with greater certainty.

What is claimed is:

1. A system for locating the points at which a drill pipe is stuck in a borehole, such system comprising:

a downhole tool having,

an acoustic section comprised of a transmitter coil and a receiver coil spaced therefrom by an acoustic isolator,

a density section comprised of a source of gamma rays, and a spaced radiation detector for measuring gamma ray radiation resulting from the induced gamma rays from the source,

electronic sections for processing the signals received by the receiver of the acoustic section and the detection of the density section,

a cable attached to the downhole tool for supporting the downhole tool in the drill pipe, the cable having an electrical conductor connected to the components of the downhole tool,

means connected to the conductor of the cable providing electrical energy to the components of the downhole tool,

means at the surface connected to the conductor of the cable receiving the signals produced by the downhole tool and processing and recording such signals to produce a log having an acoustic curve and a density curve whereby the points at which the drill pipe is stuck may be identified.

2. The system specified in claim 1 characterized in that the surface processing equipment processes only the amplitude of the first arrival from the acoustic receiver.

3. The system specified in claim 2 characterized in that the downhole tool is provided with a collar locator section comprised of a coil and magnet arrangmeent which can identify discontinuities in the drill pipe and means are provided at the surface to record the discontinuities as a separate curve on the log.

4. The system specified in claim 3 characterized in that the downhole tool is provided with at least one explosive charge arranged to be ignited by an electrically fired blasting cap.

5. The system specified in claim 4 characterized in that a safety circuit is provided for igniting the blasting cap, said circuit comprised of a DC operated relay which completes the circuit and an AC source for ignition.

6. The system specified in claim 1 characterized in that the source of gamma rays is col-limated whereby the gamma radiation is directed toward the wall of the drill pipe.

References Cited UNITED STATES PATENTS 2,659,014 11/1953 Scherbatskoy 73151 X 2,686,039 8/1954 Bender 73--151 X 3,304,538 2/1967 Zill 73151 X 3,311,876 3/1967 'Lee 73-151 X OTHER REFERENCES Caldwell, R. L.: Using Nuclear Methods in Oil-Well Logging, from Nucleonics, vol. 16, No. 12, December 1958, p. 58.

RICHARD C. QUEISSER, Primary Examiner.

JERRY W. MYRACLE, Assistant Examiner. 

